Automatic switching system



Se t. 12, 1944. B. D. WILLIS AUTOMATIC SWITCHING SYSTEM Original Filed Feb 10, 1941 7 FIG.I

5 Sheets-Sheet l NTR INVE o BERNARD D. WILLIS, DECEASED p BY w TER OWEN. EXECUT ATTORNEY Sept. 12, 1944. w' s AUTOMATIC SWITCHING SYSTEM Original Filed Feb. 10, 1941 5 Sheets-Sheet 2 INVENT OR. DECEASED LLIS R OWEN. EXECUT Sept. 12, 1944. B. D. WILLIS AUTOMATIC SWITCHING SYSTEM Original Filed Feb. 10, 1941 5 Sheets-Sheet 3 INVENTOR.

BERNARD 0. WILLIS, DECEASED I w .wA| OWEN.EXECUTOR ATTORNEY.

B. D. WILLIS AUTOMATIC SWITCHING SYSTEM Sept. 12, 1944.

Original Filed Feb, 10, 1941 5 Sheets-Sheet 4 I02 F l 6.8

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AUTOMATIC SWITCHING SYSTEM Original Filed Feb. 10, 1941 5 Sheets-Sheet 5 NE &9

A'IZTQBEX INVENT OR. BERNARD D.W|LLIS, DECEASED W WALT OWEN. EXEOUTOR mow Patented Sept. 12, 1944 UNITED STATES PATENT OFFICE AUTOMATIC SWITCHING SYSTEM Original application February 10, 1941, Serial No. 378,151. Divided and this application October 15, 1942, Serial No. 462,088

9 Claims.

The present invention relates in general to automatic switching systems, and more in particular to such switching systems as include an impulse sender or calling device at a control station, a line extending to a distant switching station or exchange, and one or more automatic switches at the latter point which are selectively controlled over the line by the calling device. at the control station.

This application is a division of applicants prior application, Serial No. 378,151, filed February 10, 1941.

An example of such a switching system is an automatic telephone system, in which each subscribers line is provided witha calling device at the subscribers telephone, and in which automatic switches are provided at the exchange for the purpose of establishing telephone connections under subscriber control. For convenience, therefore, the invention is illustrated and described herein as a simple form of automatic telephone system. It is not limited to such use, however, but may be employed in a variety of situations where it is desired to eiiect selectiveaction under remote control.

The main feature of the invention is the novel principle in accordance with which the selecting operation is controlled. In automatic telephone systems which are in common use, the control is exercised by the transmission of a variable series of impulses which are generated by a calling device. The number of impulses in a series depends on the digit in accordance with which the calling device is operated, and the selecting operation resulting from the transmission of a K series of impulses is in accordance with the number of impulses in the series. This principle of operation requires absolute accuracy in the registration of a series of impulses and since the impulses must be transmitted atrather high speed, and frequently over lines ill adapted to high speed impulse transmission, certain difficulties have been encountered which render it more or less unsatisfactory.

In applicants Patent No. 2,222,131, granted November 19, 1940,, there has been described a system of selective control for use in automatic telephone systems or other automatic switching systems, which employs a single impulse of variable length or duration, and in which the selectand is stopped at the end thereof. The switch runs at predetermined speed for the duration of the impulse, and the extent of its motion, or the selecting operation performed, is therefore in accordance with the length of the impulse. In this system of control the duration of each impulse is determined by the digit called, but is also, dependent upon the speed of the calling device, which accordingly must be coordinated with the speed of the automatic switches. in order to insure accurate selection. The necessary speed relation between the calling device and switches is not particularly difiicult of attainment, but this requirement nevertheless introduces a difficulty under certain circumstances, which renders the system less satisfactory than it otherwise would be.

My improved system of selective control resembles the system disclosed in my above mentioned patent to some extent; that is, it dispenses with the use of a variable series of impulses. At each operation of the calling device a fixed number of impulses is generated. Two impulses in stead of one are generated, however, and although these two impulses are of variable length the selection effected does not depend directly upon the length of the impulses, but upon the ratio of the length of the first impulse to that of the second. Thus the speed of the calling device, within reasonable limits, is entirely immaterial. For the digit 1, for example, the ratio of the duration of the first impulse to that of the second may be as 10 is to 1. A given calling device may operate at such a speed that the duration of the first impulse is one second, while the duration of the second impulse is one-tenth second. Another calling device may have a faster speed such that the duration of the first impulse is only one-half second, but the duration of the second impulse in this case will only be one-twentieth second, and the ratio between the two impulses will be the same.

It will be understood that in my improved system the calling device and likewise the switch under control thereof must run at some constant speed, but the two speeds do not have a fixed relation to each other and accordingly these requirements are easily met. For instance, the switch may be operated by a synchronous motor running on commercial power, which has a substantially constant frequency. The calling device, on the other hand, may be provided with a speed governor, of which several reliable types are known. Since the calling device speed is not rigidly associated with the switch speed, either speed may be varied within quite wide limits without affecting the selection control.

The practical application of the new principle of selection control described in the foregoing involves the production of a new and improved calling device and'a new and improved automatic switch mechanism, together with suitable new circuit arrangements for controlling the operations of the switch in response to the operation of the calling device. These may be regarded as additional features of the invention.

The foregoing and other features of the invention will be fully explained in thecourse of the following detailed description, reference being had to the accompanying drawings, in which:

Fig. 1 is a front view of the calling device;

Figs. 2 and 3 are additional views of the calling device, Fig. 2 being a section on the line 22, Fig. 3, and Fig. 3 being a section on the line 33, F

Figs. 4 and 5 are fragmentary views showing details of the calling device;

Fig. 6 is a partial section on the line 6-6, Fig. 3, showing the commutator;

Fig. 7 is a side view of the switch mechanism;

. Fig. 8 is a section on the line 8-3, Fig. 7;

Fig. 9 is a view showing details of the switch brush construction;

Fig. 10 is a partial end view of the switch showing the electromagnetic operating mechanism;

Fig. 11 is a vlew showing details of the main drive rollers; and

Fig. 12 is a diagrammatic circuit drawing of an automatic telephone system in accordance with the invention.

Referring to Figs. 1 to 6, inclusive, the calling device will first be described. Fig. 1 shows the general appearance of the calling device when installed and ready for use. As seen inthis figure, there is a base I, which may be a metal casting, and which is provided with rubber supports 3 at the corners. There is also a cover 2, of heavy sheet metal, and shaped as shown in Figs. 1 and 2. It will also be seen that a number of digit keys such as key I are provided, which project through slots such as 8 in the curved front of the cover 2. There may be ten of these keys, numbered from 1 to 0, inclusive. At the left of the row of keys there is an escutcheon 5, which holds the directory card '6. At the right hand end the cover is completely closed, but at the left hand end there is a circular opening (see Fig. 3), which is provided in order to afford access to the rear of the commutator Ill for wiring purposes. This opening is closed by a detachable shallow cup-shaped closure member 4.

Most of the parts of the calling device are mounted on the base I. To this end a U-shaped bracket 18 is provided at one end of the calling device and an L-shaped bracket II at the other end. There is also an L-shaped bracket 45. These brackets may be fastened to the base I by means of screws, as indicated in Fig. 3. The shaft I2 is supported in bearings in the two brackets Hi and l I and supports the gear wheellB. The ten digit keys such as key I are also mounted on the shaft [2 a The arrangement of key 7 may be described in detail in connection with Fig, 4. Reference may also be made to Fig. 2 which shows the key in operated position. At the projecting extremity of the key there is a knob or ball 3|, secured to the shank of the key by a screw 32. At the other end the key is provided with a hub 36, which is rotatable on the shaft [2. Projecting downwardly and to the right from the hub 36 there is an arm 39, provided for the purpose of controlling the.

contact spring 4!, which is maintained normally separated from contact spring 42. A coil spring 46, better seen in Fig. 2., is attached to arm 39 and tends to rotate the key in a clockwise direction on shaft l2, thereby normall maintaining it in the position in which it appears in Fig. 4. The key I is also provided with a locking hook 33, the purpose of which will be described subsequently.

Associated with the key I there is a disk 31, which is keyed or otherwise rigidly secured on shaft l2. The disk 37 has four notches spaced ninety degrees apart around its periphery, whereby it may be rotated by the key a through the medium of the pawl 34, the latter being held against the disk by the spring 35. The slot 8 is long enough so that when the key I is operated (see Fig. 2), it moves through an arc of somewhat more than ninety degrees. Each time the key is operated, therefore, the pawl 34 engages in one of the notches 38 and rotates the disk 3? through an angular distance of ninety degrees. The rotation of the disk of course rotates the shaft l2, since the disk is fixed to the shaft.

Each ofv the other keys is arranged the same as key I, and each of these other keys has associated with it a notched disk similar -to the disk 31. When any key is operated, therefore, the shaft i2 is rotated through an angular distance of ninety degrees.

The key locking mechanism will now be described. It comprises a shaft l4, rotatable in bearings in the brackets I0 and II, two arms 26 and 28, which are rigidly secured toshaft It by keyed hubs 2'! and 29, and a cross rod 30 which extends between the ends of arms 25 and 28 and is rigidly secured thereto. Associated with the arm 26 there is a coil spring 45, which tends to rotate the arm 26 and shaft M in a clockwise direction,

such rotation being limited, however, by a stop screw 44 which prevents rotation of the arm 26 beyond the position in which it is shown in- Figs. 2 and 4. There may be a similar'stop screw and spring associated with the arm 28, as indicated in Fig. 3. With this locking arrangement, it will be seen that when any key such as 7 is operated, its locking hook such as 33 .will depress the cross rod 30, rotating the shaft 14 through the medium of arms 26 and 23. When the hook passes the cross rod, the latter is raised again by the springs such as 45 and the key is locked, as shown in Fig. 2.

The contact springs 4| and 42 associated with key 1 have already been referred to. There is a similar set of contact springs associated with each of the other keys. These sets of contact springs are all mounted by suitable screws and insulators on a fiat metal bar 50 which may be formed integrally with the channel member 5!.

The latter extends lengthwise along the rear of the cover 2 on the outside thereof and forms a conduit for the conductors which lead from the sets of contact springs to the commutator H1. The channel member 5|, bar 50, and the sets of contact springs constitute a demountable unit which may be assembled and wired outside the calling device. When this unit is to be assembled in the calling device the bar 50 and associated sets of contact springs are passed through an opening which is provided in'the rear wall of the cover 2. This opening is closed by the channel member 5|, the cars such as '52 and 53 of which now rest against therear wall of the cover.

The unit is held in position by meansof screws such as 54 and 55." It will'be understood that each set of contact springs is controlledby its associated key in sucha manner that the springs are normally open, being allowed to close, however, whenever the key is operated. The open and closed positions of'the set' of contact springs 4 I42 are shownin Figs. 4 and 2,- respectively.

Supported in bearings von'the brackets Iand 46 there is a short shaft I8; The shaft I8 is adapted to be rotated'by apinion I 5, which isin mesh with thegear'wheel I3. The gear ratio is four'to one, from which it follows that. the pinion I5 and shaft I8 arerotated three hundred and sixty degrees, or one complete rotation, each rigidly fixed to the gear wheel 43 andprojects from the side thereof, as shown in Fig. 3. The spring I6 is normally under tension, tending to rotate the gear wheel 43 in a clockwise direction, as seen in Fig. 2. Rotation of the gear wheel cannot normally take place, however, due to the fact that the pin IT is held by the hook 51 on the end of arm 56, as shown in Fig. 4. The arm 56 is rigidly supported on shaft I4. Since the spring I6. is under tension, it also tends to rotate the shaft I8 and pinion I5 in a counterclockwise direction, but such rotation is prevented by the dog 59, Fig. 2, which engages with the teeth of the gear wheel I3.

The gear wheel 43 is in engagement with a pinion 20, which is fixed on the shaft IS, the latter having bearings in the bracket I0. On this shaft there is mounted the wind governor comprising vanes 2|. Any other known form of governor could be used here, such as a centrifugal governor, for example.

The commutator I0 may be of molded insulating material and has a row of contacts BI to 60 and H embedded therein, as seen in Figs. 3 and 6. There is also a ring I2 of conducting material. The commutator may be secured to the cover 2 by means of screws, as shown in Fig. 6.

The gear wheel 43 carries a pair of brushes 24 and which cooperate, respectively, with the contacts such as BI and the ring I2. These brushes are supported in brush holders 22 and 23, which are insulated from the gear wheel, but are conductively connected together. The brush 24 is normally in engagement with contact II, and this contact is therefore normally connected through the two brushes to ring 12. When the gear 43 is rotated, the brush 24 leaves contact II and engages successively with contacts 60, 69, etc., which are thus connected successively to ring I2, since brush 25 maintains continuous contact with the ring.

The contacts such as II are each provided with a pin or stud such as I3, these pins extending through the commutator and projecting from the back thereof. There is also a pin 14 associated with the ring 12. able suitable circuit'connections to be made to the commutator.

The wiring is shown in Fig. 12, where the call ing device is shown diagrammatically and is indicated by the reference character CD. As

These pins enshown, there are only. two conductors leading in to the calling device, these conductors being indicated at 202 and 203. These conductors extend through a suitable opening in the closure member 4 (see Fig. 1), to the rear of the commutator I0, where conductor 202 is connected to the ring I2 by means of the pin I4. Conductor 203v is connected to contact H by means of its pin -13. This pin 'I3.is also connected to all of the contact springs such as 42 of the sets of contact springs which are associated with the keys. The other contact springs such as 4| of these sets of contact springs are wired individually to the pins such as 13' which are associated with the commutator contacts GI to 60. That is, contact spring 4| associated with the first key I corresponding to the digit 1 is wired to contact BI, the contact spring corresponding to spring 4I'but associated with the digit 2 key is wired to contact 62, and so on. There being ten keys, there will be ten conductors connected as described. These conductors, together with the additional conductor for connecting the contact springs such as 42 with the contact II, extend from the key contact springs by way of the conduit 51 and the extension 4' of the closure member 4 to the rear of the commutator, where they are connected as described.

Reference may now be made to Figs. '7 to 11, inclusive, which show a complete switch constructed in accordance with the invention.

The various parts of the switch are mounted on a frame which comprises a flat metal plate l0land a second metalplate I02 which is bent as shown in Fig. 8 and secured to plate IN by means of screws.

The switch bank comprises an arcuate-shaped member I04 having on the face thereof a plurality of contact sets such as I05. The member I04 is preferably of molded insulating material, with the contacts such as I05 embedded therein, each contact having a pin which projects at the rear of the member I04 for the attachment of a conductor. The bank may, however, be constructed in other ways, as is well known in the art.

The switch bank is secured to the frame by means of two brackets I06 and I01, as seen in Fig. '7. The bracket I06 includes a part which rests against the frame plate I0! and which is secured to plate IOI by screws, a second part extending at right angles to the first part and parallel to the plane of the paper, a third part extending forward perpendicular to the plane of the paper, and a fourth part extending parallel to the plane of the paper to which the end of the bank I04 is secured by screws. The bracket I01 includes a part secured to the frame plate I02 by means of screws and a forwardly offset part to which the lower end of the bank is secured by screws.

The end of frame plate I02 is bent forward at right angles to form a bearing member I03. The shafts III] and III extend through bearing in the frame plate IIII and parallel to the frame plate I02, and are provided with bearings in the member I03. These two shafts support a movable carriage I I2 which is threaded on the shaft H0 and which is slidable on the shaft III. It will be understood that shafts H0 and III pass through openings in the carriage, and that the threaded opening provided for the threaded shaft I If? affords means for moving the carriage to the right upon rotation of shaft I I0, the carriage sliding on shaft I I I in the course of such movement.

The bevel gear H4 is also slidable on shaft III. The shaft III is adapted to'rotate the gear H4 in any position of the carriage through the medium of a square spline II9 which lies partly in the groove I I3 and partly in a corresponding recess in the gear, to which it is secured by a screw I20.

Extending vertically upward from the carriage H2 there is a shaft or rod II6 which is rigidly fixed to the carriage. The block H8 is slidable vertically on the rod I I 6. There is also a vertical rotatable shaft II1, which is threaded in the block I I8 and which has a bearing in the carriage I I 2. The shaft I I1 is rotated by means of a bevel gear H5, in mesh with gear H4, and such rotation is effective to raise the block H8, sliding it along the rod I I6.

The reference character I2I indicates a pivoted wiper or brush arm. At the left this wiper arm is bent in a U shape, forming a short section I32 which is parallel to but offset from the main part of the wiper arm, as seen clearly in Fig. 8. The support I30 is secured to the frame plate IOI as shown, and is bifurcated, whereby two downwardly extending members I33 and I34 are formed, which lie on opposite sides of the section I32 of the wiper arm. The pivot pin I3I passes through these parts and affords a bearing or pivot about which the wiper arm I2I is rotatable.

The wiper arm I2I has a slot I22, as clearly shown in Fig. 7. The pin I35, Fig. 8, i rigidly fixed to the block H8 and projects through the slot I22 in the wiper arm. When the carriage I I2 is moved to the right, the pin I35 slides along the slot I22, and when the block II8 slides vertically on the rod II6 the pin I35 rotates the wiper arm I2! on its pivot I3I.

The three wipers or brushes are indicated at I23, I24, and I25. At the right hand end the wiper arm I2I includes an offset portion I31, to which there is secured a block of insulating material I26. The wiper I23-I25 are secured to this block, as shown clearly in Fig. 9. i

The rod I38 extends diagonally across the switch, as shown in Fig. 7, and is pivoted on frame plate IOI at I39. The lower end of the rod rests normally against the insulated support I4I The pivot I39 is also insulated, so that the rod is electrically insulated from the frame and other parts of the switch. A terminal member I 40 is clamped to the rod near the pivoted end thereof and provides means for attaching a conductor. a

The arrangement for rotating the shafts H and III may now be described, with reference Briefly stated,

particularly to Figs. and 11. this arrangement comprises a power driven roller I50 which is adapted to be brought into engagement successively with rollers I5I and I 52, which are mounted on shafts H0 and III, respectively. 1 The roller I50 is supported on a pivoted arrnature E51. The armature I51 is operated by two electromagnets I53 and I54, the cores of which are attached to the plate I14. The latter is set edgewise against the frame plate IOI and is fastened thereto by screws. The armature I51 lies in a slot in the plate I14 and is provided with a pivot I15. The armature I51 includes an extension I60, which is bifurcated as shown in Fig. 11, the extension thus comprising the two members "SI and I62 which are provided with bearings for the shaft I 63 on which the roller I50 is mounted. The shaft I63 is connected to a short flexible shaft I64,.which is continuously rotated at a constant speed by any suitable means provided for that purpose. The shaft I64 may, for instance,

be driven by a small motor, or a plurality of such shafts associated with a plurality of switches may be geared to a common motor driven shaft. Such arrangements for driving switches of the power operated type are well known and accordingly are not shown herein.

From the foregoing it will be understood that the roller I50 i continuously rotated at the desired speed by the shaft I64. The rotation of roller I50 is normally ineffective, however, for it is normally out of engagement with both of the rollers I 5| and I 52, being maintained in a central position by means of springs I58 and I59 which are attached to the armature I51. To guard against accidental movement of the armature I51 on its pivot, by shock or other cause, such as might bring about a momentary engagement between roller I 50 and roller I5I or roller I52, a light auxiliary armature I12 may be provided. This armature is pivoted on the main armature I51 and is normally maintained at right angles thereto by a spring I13, whereby the ends of the auxiliary armature are adapted to engagethe ends of the brackets I65 and I66 and positively prevent any undesirable movement of the main armature on its pivot. When the electromagnet I53 is energized, the pole piece I55 first operatively attracts the adjacent end of the auxiliary armature I12, which is thus rendered ineffective to prevent the movement of the main armature I51 toward the pole piece. The operation of the The bracket I65 not only acts as .a stop in cooperation with the auxiliary armature I12 but also serves to support a pair of contact springs I61 and I68. These contact springs are normally in engagement but are separated by a knob of insulating material I1I whenever the armature I51 is operated by the electromagnet I53. A similar set of contact springs I69 and I10 is supported on bracket I56. These springs also are normally closed and are separated by knob I1I whenever the armature I51 is operated by electromagnet I54.

The electromagnets I16 and I 11 are brake mags nets and are provided with armatures I60 and HI which are adapted to engage the rollers I52 and 55!, respectively, to prevent rotation thereof, as will be subsequently explained more in detail. The magnets I16 and I1! are mounted on the frame plate I0! by means of brackets I18 and H9, respectively.

The carriage I I2 is normally maintained in its extreme position to the left where it bears against the frame plate Mil by a clock spring I9I, which tends to rotate the shaft H0 in a clockwise direction as viewed from the right hand end of the shaft in Fig. '2. A similar clock spring I tends to rotate the shaft H! in the same direction, which maintains the block I I8 in a position where it bears against the top of the carriage IIZ. A 7

pair of off normal springs, comprising the contact springs I65 and I86, are normallymaintained open by the block l 58. These springs may be mounted on the frame plate IOI, as'shown in Fig. 7.

.Reference may now be made to the circuit drawing, Fig. 12, which shows the electrical con nections of the system; 7

The reference character A indicates a telephone, which may be of any suitable common battery type. The conductors 200 and 20! extend from the telephone to a terminal strip 204, where the conductors 202 and 203 coming from the calling device CD are also terminated. At this terminal strip conductor 200 is connected directly to the line conductor 205, while conductor 29! is connected to the line conductor 206 by way of the calling device CD. In other words, the calling device is connected in series with one side of the line.

The line conductors 2G5 and 20B extend to a switching station or exchange where they terminate in an automatic switch indicated by the reference character S. This switch comprises a switch mechanism such as is shown in Figs. 7 to 11, inclusive, and the control relays 2 iii to 21s, inclusive. The functions of these relays will be explained shortly.

The switch S may have access to ten lines, one of which is shown, and comprises the line conductors 227 and 228. These conductors may extend to a telephone station B, which may be a common battery telephone similar to the telephone A. The relays 220 to 223, inclusive, are at the e cha e and are individual to the line of station B.

A suitable source of current is provided for operating the switch, such as a storage battery, for

example. In the circuit drawing connections to the negative pole of the battery are indicated by arrows accompanied by negative signs, while connections to the positive or grounded pole of the battery are indicated by the usual ground symbols.

The operation of the system will now be described, it being assumed for this purpose that a call is to be made from the station A to th station B. The line of station E is connected to the first set of bank contacts in the switch S and accordingly is selected by calling the digit 1. When the receiver is removed at station A, a circuit is completed for the line relay 2| 1, said circuit extending from ground by way of the lower winding of the line relay, contact 23!, line conductor 2G6, conductor 263, contact H, brushes 24 and 25, ring 12, conductor 202, conductor 20], telephone at station A, conductor 200, line conducto 205, contacts controlled at 230, and the upper winding of relay 2H to negative battery. Upon energizing, the line relay 2!! closes a circuit for the slow-acting relay 212 at contact 232, said circuit also including contact 243. Upon energizing in turn, relay 2l2 prepares certain circuits at contacts 234 and 235, and at contact 238 closes circuits for the brake magnets I16 and I'll. These circuits include the set of contact springs controlled by the armature l! and will be apparent upon inspection. The brake magnets energize when their circuits are closed and their armatures grip the rollers I52 and [EL The calling party at station A may now '01:)- erate the calling device key corresponding to the digit 1, rotating this key forward from its normal position as shown in Fig. 4 to the fully operated position in which it appears in Fig. '2. The operation of the key rotates the shaft [2 through an angular distance of ninety degrees, and gear [3 and pinion l5 cause one full rotation of shaft 18, thereby winding spring it. As the key approaches its fully operated position the hook 33 depresses the locking bar 30, as s ow in Fig. 5, thereby rotating shaft I4 and arm 56 and moving the hook 5! far enough to the left brush 24.

so that it can no longer hold the pin l1. This operation releases the gear 43, which starts to rotate in a clockwise direction from power supplied -by spring l6 and under the control of the governor 2i. When the key reaches its fully operated position, the shaft I4 is restored by spring and the key becomes locked by bar 30, as shown in Fig. 2. The operation of the key permits contact spring 45 to engage contact spring 42, thereby connecting contact Bl to the conductor 203.

When the gear 43 is released as described in the foregoing, it makes one complete rotation and then becomes locked in normal position, the

operated key -'I being released just before the gear wheel has fully returned to normal, The manner in which these operations take place will be readily understood from the drawings, particularly Fig. 5. When the gear wheel approaches normal position and shortly before the pin I1 reaches its dotted line position, the said pin engages the cam surface 58 on arm56, whereupon the further rotation of the gear wheel rotates shaft 54 and depresses the locking bar '30. This operation releases the operated key, which is restored to normal position by the spring 40. As soon as the pin ll passes off the cam surface 58, the shaft I4 is restored instantly, the arm 55 is moved to the right, and the pin l'l passes into the notch behind hook '51. The gear wheel 43 thus becomes locked again, as shown in Fig. 4. After the key'has been released, reverse rotation of the shaft [2 and gear [3 is prevented by the dog 59. The slight retrograde movement that may occur before the dog engages a tooth of gear l3 does no harm because of the fact that the keys move through an arc which is greater than ninety degrees.

During the rotation of the gear wheel 43 the brushes 2'4 and 25 cooperate with the commutator contacts to transmit two impulses over the line to effect the desired control over the switch S, whereby the said switch is caused to select the line of station B. These so-called impulses are actually interruptions of the line circuit. When the brush 24 leaves contact II the line circuit is opened, starting the first impulse. As the brush 24 engages contact 60, 69, etc., the line circuit remains open, for these contacts correspond to the tenth, ninth, etc. digit keys, which are in normal position. When brush 24 reaches contact 6i, however, corresponding to the first digit key, the line circuit is again closed, for-contacts 4| and 42 have been closed by the operation of the key. Theengagement of brush 24 with contact 6| thus terminates the first impulse. The line circuit is again opened when the brush 24 leaves contact 6 l, which thus starts the second impulse. This impulse is terminated when the brush 24 reaches contact H, where it comes to rest.

When the calling device is operated in accordance with the digit 1, that is, when the first digit key is operated, the two impulses resulting from the operation bear a ratio to each other which is as ten is to one. Explaining this more in detail, the path of the brush 24 is divided into thirteen equal spaces. One of these spaces is occupied by the normal position contact Il, leaving twelve spaces in which the line circuit may be interrupted when such spaces are traversed by Ten of these spaces are occupied by the contacts '6! to 50, inclusive, there being a blank space on either side of the contact H. These spaces correspond to time units, since the brake magnet I11.

brush moves at constant speed. Thus it will be seen that during one complete rotation of the brush 24 the line circuit will be opened at contact H for a total period of twelve time units. The line circuit is not actually open for this whole period, however, for in the rotation of the brush it will pass over an active contact such as SI, thereby closing the line circuit for an interval of one time unit and dividing the total period of twelve time units into two complementary impulse periods, the sum of which is equal to eleven time units. In case the digit 1 is called, contact 6! is rendered active, and the first impulse comprises ten time units corresponding to the angular distance from contact 1! to contact BI in a clockwise direction, while the second impulse comprises one time unit, corresponding to the angular distance from contact (H to contact 1| in a clockwise direction. If the digit 5 is called, the contact 35 is made active, the first impulse will be six time units in duration, and the second impulse will have a duration of five time units. The impulse ratio in this case is six to five. The impulse ratios corresponding to the otherdigits will be apparent from the foregoing and are seen to range from ten to one (digit 1) to one to ten (digit Proceeding now to a consideration of the operation of the switch S in response to the impulses, the first impulse or interruption of the line circuit causes the line relay 2i I to deenergize and the circuit of relay H2 is broken; Since the latter relay is slowv acting',,however, it does not fall back immediately, and a circuit is closed for the magnet I53, said circuit extending from ground by way of contact 243, contact 232, contact 234, contact 231, winding of relay 2l5, and winding of magnet I53 to negative battery. Relay 2I 5 is energized over this circuit and prepares a circuit for the change-over relay 2I3 at contact 242.

When the magnet I53 is energized, it operates the armature I51, thereby bringing the continuously rotating roller I50 (see Fig. into engagement with the roller I5I. At the same time the armature I51 separates the contacts I61 and I68, thus deenergizing the brake magnet I 11, and freeing the roller I5 I. The roller I5| according- -ly starts to rotate the shaft H0, winding spring I9I, and the carriage II 2 starts to moveto the right. As soon as the carriage has moved off normal the contact springs I85 and I 85 are closed, thereby completing a locking circuit for relay 2I2. This relay accordingly remains energized throughout the first impulse, regardless of its 7 duration.

At the end of the first impulse the line circuit is closed and the line relay is again energized, breaking the circuit of relay 2I5 and magnet I53. Relay 2I5 is slow acting and holds contact 242 closed long enough so that the line relay can .close a circuit for relay 2I3 at contact 233. Upon energizing, relay 2I3 locks itself at contact 238. The magnet I53 deenergizes when its circuit is broken, whereupon the armature I51 is retracted and the roller I50 is disengaged from roller I5I. vAt the same time the contact springs I 61 and I 68 are allowed to close, thus again energizing the The brake magnet I11 now prevents reverse rotation of the shaft IIO by the spring ISI.

During the first impulse the carriage H2 is moved continuously to the right by the rotation of the shaft H0, and the pin I in the block II8 The distance traversed, of course, depends on the speed of the switch drive, which should bear such a relation to the calling device speed that the pin I35 will travel the greater part of the length of the slot, the exact distance being immaterial within a considerable range. It may be assumed that when the first impulse is terminated the pin I35 has reached the point X; that is, it traverses the distance OX, the point 0 representing the travels along the slot I22 in the wiper arm 12L initial position of pin I35.

When the second impulse is received the line relay 2! I is again deenergized, and opens the circuit of relay 2 I2, also the circuit of relay 2 I 3, but these relays remain energized over their locking circuits. The line relay also closes a circuit for the magnet I54, extending from ground by way of contact 243, contact 232, contact 234, contact 231, winding of relay 2M, and winding of magnet I54 to negative battery. Relay 2M energizes over the above circuit and at contacts 239, 240, and MI disconnects the switch Wipers I23, I24, and I25.

The magnet I 54 is also energized, and operates armature I51, thereby causing the roller I50 to engage the roller I52, and at the same time separating the contact springs I69 and I10. The brake magnet I16 is thus deenergized and the rollers I50 and I52 start to rotate the shaft III. The shaft III rotates the shaft II! by means of gears H4 and H5, thereby raising the block H8 and pin I35 and rotating the wiper arm l2! about its pivot I3I. This pivot does not appear in the circuit drawing, Fig. 12, but is in alignment with the pin I35 when the latter is in normal position, as will be recalled from Fig. 8.

At the end of the second impulse the line relay again energizes, breaking the circuit of relay 2I4 and magnet I 54. Upon deenergizing, relay 2I4 connects up the wipers I23, I24, and I25. When the magnet I54 deenergizes, the armature I51 is retracted, disengaging the roller I50 from roller I52 and closing the contact springs I69 and I10, The rotation of shafts III and H1 is thus terminated and the shafts are held in their advanced positions against the tension of spring I00 by the brake magnet I16, which energizes again as soon as contact springs I89 and I10 are closed.

The second impulse is'only one-tenth as long as the first impulse, and consequently the vertical distance traversed by the pin I 35 is only onetenth of the horizontal distance. This vertical distance is represented by the distance XY, which is one-tenth the distance OX, The final position of the pin I35 is therefore at the point Y, and the wiper arm is positioned along the line OY, bringing the wipers I23, I24, and I25 into engagement with the first set of contacts in the bank of the switch.

The relay 2I4 does not fall back until after the switch wipers have been brought to their final selective position. The contacts 239, 240, and MI then close, and the line conductors 205 and 206 are extended by way of contacts 240 and 24I, wipers I24 and I25, bank'conta'cts 254 and 255, and conductors 224 and 225 to the windings of the line relay 220. Relay 220 is accordingly energized over the calling line in parallel with the line relay 2 and closes a circuit for the ringing relay 223 at contact 250. Upon energizing, relay 223 connects a source of ringing current Gen. to the conductor 221 and 228 of the line extending to station B, said connection being made at contacts 263 and 264, and at contact 262 connects ground to the holding conductor 226. The grounding of conductor 226 operates relay 22I, which looks itself to ground at contact 260 of relay 220' and breaks the circuit of relay 223. The latter relay is slow acting and holds the ringing circuit closed for an interval after its circuit is broken. After relay 223 has deene'rgized the holding conductor 226 is maintained grounded by way of contact 260 of relay 220 and contact 26I of relay 22 I The grounding of the holding conductor 226' completes a circuit for relay 2"], extending from ground on said conductor by way of bank contact 253, wiper I23, contact 239', and winding of relay 2I0'to negative battery. Upon energizing, relay 2I0 disconnects the line relay 2| I from line conductors 205 and 206 at contacts controlled at 230 and at contact 23l, and at contact 230 closes a local circuit for the line relay including the resistance 245. The line relay 2H is thus held energized.

When the call is answered at station B, the calling and called parties may carry on a conversation in known manner. Current for the transmitter at station B is supplied through the windings of the impedance coil 222, while current for the transmitter at station A is supplied through the windings of the line relay 220.

The release of the connection is brought about by the replacement of the receiver at the calling station A. When the receiver is replaced, the line circuit is interrupted and the line relay 229 is deenergized, opening the circuit of relay 22I and removing ground from the holding conductor 226. Relay 2I0 accordingly deenergizes and breaks the circuit of the line relay 2| I. Upon deenergizing, the line relay closes the previously described circuit including relay 2M and magnet I54, the said relay energizing and disconnecting the switch wipers as before. Magnet I54, upon energizing, brings rollers I50 and I 52 into engagement and also opens contact springs I69 and IIIl'to deenergize the brake magnet I16. Rotation of shafts III and II! now ensues, which raises the block H8 and pin I35 in the manner previously described. The movement of the block and pin continues until the latter engages the rod I38, whereupon a circuit is closed for relay 2I6, extending from the grounded frame of the switch by way of pin I35, rod I38, and winding of relay 2I6 to battery. Upon energizing, relay 2I6 locks itself at contact 244, and at contact 243 it breaks the circuit of relay 2I4 and magnet I54 and also the circuits of the brake magnets I16 and III. The deenergization of magnet I54 disengages the roller I50 from roller I52 and stops further upward movement of the block I I8. The deenergization of the brake magnets leaves the shafts H and I I I free, with the result that they are rotated in the reverse direction by the springs I9I and I90. Thus the block H8 is lowered until it again rests on top of the carriage II2, while the latter is moved to the left until it engages the frame plate IOI. The Wiper arm rotates on its pivot in response to the movement of block H8 and assumes a horizontal position.

The restoration of the mechanical parts as described in the foregoing separates the off normal springs I85 and I86, thereby breaking the locking circuits of relays 2I2, 2I3, and 2| 6. These relays therefore deenergize and the switch is com pletely restored to normal, ready for another call.

The manner in which the switch is operated in response to the calling of other digits will be :readily understood. When the digit '7 is called,

for instance, by operation of the digit key corresponding to the digit '7, the calling device CD transmits two impulses having an impulse ratio of four to seven. In response to the first of these impulses the carriage I I2'moves to the right during an interval of four time units and the pin I35 reaches the point X. In response to the second impulse the block IIB moves vertically during an interval of seven'time units and car-- ries the pin I35 to the point Y. is rotated during the movement of block I I8 and takes up a position along the'line O--Y', thereby positioning the wipers on the seventh set of bank contacts. The other digits are called in.

the same way. It may be stated'generally that the impulse ratio is different for each digit and, that when any digit is called the pin I35 of the switch is moved along the two sides of a right triangle in which the lengths of the sides bear the same ratio to each other as the impulse ratio. The wiper arm is in any case positioned along the hypotenuse of the triangle, a line the slope of which is determined by the relative lengths of the sides and not by their absolute lengths.

It will be easily seen now why the speed of the calling device can be varied independent of the switch drive speed without affecting the accuracy of selection. Suppose, for example, that the calling device speed increases, which will decrease the length'of the impulses, although maintaining the same ratio between them. It may be assumed that the increase in speed is so great that when the digit 7 is called the length of the first impulse is only sufficient to advance the pin I35 to the point X instead of to the point X. The second impulse is correspondingly shortened, however, so that in its vertical movement the pin I35 is raised only to the point Y". The point Y lies on the line O--Y, from which it will be seen that the final position of the wiper arm is the same regardless of the change in the speed of the calling device.

It will be appreciated that, while a comparatively simple telephone system has been shown herein, the principle of selection disclosed may be used in larger systems, following known methods employed in expanding the capacity of automatic telephone systems in common use. It will be understood also that this new principle of selection may be employed to advantage in var-- ious other automatic switching or indicating sys tems, and in such cases the number of selections: or the number of calling device keys may be: increased beyond the number shown herein. Nor is the invention limited to the precise impulse ratios explained herein, which have been selected. merely as a convenient illustration of the prin ciple involved.

Various other modifications may be made within the spirit of the invention, and applicant does not therefore wish to be restricted to the exact form of the invention which is shown and described herein, but desires to include and have protected by Letters Patent all forms and modifications of the invention which come within the scope of the appended claims.

What is claimed is:

1. In an automatic selecting device, a carriage, means including a threaded rotatable shaft for moving said carriage, a second rotatable shaft on which said carriage slides during such movement, a third shaft having a bearing in said carriage and geared to said second shaft, a member threaded on said third shaft, means for rotating said second shaft to move said member,-

The wiper arm.

by means of said third shaft, and a pivoted selecting element controlled by the movement of said member.

2. In an automatic selecting device, a pivoted selecting element, a control member normally stationed at the pivot point of said element, a threaded rotatable shaft for moving said member along said element to diiferent positions with respect to said pivot point, a second shaft threaded through a hole in said member and extending at right angles to said first shaft, and means for rotating said first shaft to slide the member along said elementto one of its positions and for then rotating said second shaft to cause said member to engage with and rotate said se' lecting element about its pivot,

3. In an automatic selecting device, a pivoted selecting element, a control member located at the pivot point of said element, means for causing a rectilinear movement of said member through variable complementary distances in directions at right angles to each other, said movement causing an adjustment of said selecting element to a position determined by a line passing through said pivot point and the final position of said control member. 7

4. In an automatic selecting switch, a plurality of contacts, a pivoted wiper having access to said contacts, operating means for moving said wiper to select one of said contacts, means for moving said operating means to different points relative to said wiper without operating the wiper and means for then moving the operating means to move the wiper to a' point determined by both movements of the operating means.

5. In an automatic selecting device, a wiper, an operating member therefor, a worm, means for turning said worm to move said member relative to the wiper without moving the wiper, a second worm, and means for turning said second worm to again move said member to in turn move said wiper to a point dependenton both movements of said member.

6. In a selecting switch, a wiper, contacts accessible thereto, an operating member therefor, means for moving said member in one continuous linear movement in one direction and then in a second continuous linear movement in a plane at right angles to the plane of said first movement, to thereby move said wiper in one continuous movement over said contacts to select a particular one thereof.

'7. In a switching mechanism having a bank of contacts and a pivoted wiper capable of rotational movement to connect with any of its contacts, an operating mechanism for said wiper comprising a pair of parallel rotatable shafts, a Wiper moving element movably mounted on said shafts, means for rotating one shaft to move the element in a direction parallel to' the axis of said shafts, and means for then rotating the other of said shafts to move the element in a direction at right angles to its first movement, said last movement causing rotation of the wiper to engage one of its contacts.

8. In a selecting device, a pivoted selecting element, a worm gear, a rotatable shaft, a car.- riage slidably mounted on said rotatable shaft, means for rotating said gear to slide said carriage along said shaft to different positions, a worm shaft mounted on said carriage and geared to said rotatable shaft, an operating member for the element mounted on said worm shaft and movable longitudinally thereon when the worm shaft is rotated, and means for rotating said rotatable shaft, after the carriage has been moved to one of its positions, to turn said worm shaft to in turn move said member to thereby move said selecting element to a desired position.

9. In a selecting mechanism, a wiper arm carrying wipers at one end and pivoted at the other end, contacts accessible thereto, an operating element for moving said arm through variable distances to engage different sets of 'contacts, means for first moving said element longitudinally of said arm to points having different leverage thereon, and means for then moving said element transverse to said arm to carry the same a certain distance as determined by the longitudinal movement thereof.

' WM. WALTER OWEN, Executor of the Estate of Bernard D. Willis, De-

ceased. 

